1. Field of the Invention
The present invention relates to a fuel pump that has a motor arrangement and a pump arrangement.
2. Description of Related Art
For instance, Japanese Unexamined Patent Publication No. 2005-110477 and Japanese Unexamined Patent Publication No. 2005-110478 (corresponding to US 2005/0074343 A1) recite a fuel pump, which includes a brushless motor to form a motor arrangement that drives a pump arrangement. In this fuel pump, fuel, which is pumped by the pump arrangement, passes through an interior of the motor arrangement. In the brushless motor, there is no disadvantageous loss caused by a sliding resistance between a commutator and brushes, an electric resistance between the commutator and the brushes and a flow resistance experienced by the respective groove between segments of the commutator, which all occur in a brush motor. As a result, a motor efficiency of the brushless motor is higher than that of the brush motor, and thereby an efficiency of the above fuel pump is improved. The efficiency of the fuel pump is a ratio of a work output of the fuel pump, i.e., a value of (a fuel delivery pressure)×(a fuel delivery quantity) with respect to the amount of electric power supplied to the fuel pump. In a case where the efficiency of the fuel pump is increased under the same work output, the size of the motor arrangement can be reduced to downsize the fuel pump when the brushless motor is used in the motor arrangement instead of the brush motor. Furthermore, when the efficiency of the fuel pump is increased, the electric current supplied to the fuel pump can be reduced to reduce the electric power consumption of the fuel pump. The fuel pump, which uses the brushless motor to reduce its size and its electric power consumption, is particularly suitable for a small motorcycle, which has a relatively small fuel tank and a small electric supply power.
In the case of the fuel pump, in which fuel pressurized by the pump arrangement passes through the motor arrangement, it is desirable to limit contact between coils of the motor arrangement and the fuel. In Japanese Unexamined Patent Publication No. 2005-110477 and Japanese Unexamined Patent Publication No. 2005-110478, the stator of the motor arrangement is covered with resin to limit contact between the coils of the stator and the fuel. Furthermore, in Japanese Unexamined Patent Publication No. 2005-110477 and Japanese Unexamined Patent Publication No. 2005-110478, the gap, which is formed between the stator and the rotor, is used as a fuel passage for conducting the fuel that flows through the motor arrangement.
However, in the structure of Japanese Unexamined Patent Publication No. 2005-110477 and Japanese Unexamined Patent Publication No. 2005-110478, when the size of the gap is increased to create a sufficient passage cross sectional area for achieving the required fuel delivery quantity of the fuel pump, a magnetic force between the rotor and the stator is reduced to disadvantageously reduce the efficiency of the fuel pump.
In contrast, when the size of the gap between the stator and the rotor is reduced to increase the magnetic force between the rotor and the stator, the passage cross sectional area of the fuel passage, which is formed between the stator and the rotor, is reduced. As a result, the passage flow resistance is increased to disadvantageously reduce the efficiency of the fuel pump, and the required fuel delivery quantity may not be achieved in some cases.